Correlation of size and photoluminescence for Ge nanocrystals in SiO 2 matrices

Abstract

Synthesis and size-dependent photoluminescence has been performed for Ge nanocrystals in SiO 2 matrices with average diameters between 2 and 9 nm, formed by room-temperature ion implantation into SiO 2 followed by precipitation during vacuum thermal anneals. Nanocrystal size distributions obtained from electron microscopy data were used in conjunction with a quantum-confined exciton recombination model [T. Takagahara and K. Takeda, Phys. Rev. B 46 (1992) 15578] to generate calculated photoluminescence spectra, which were compared with experimental spectra. Qualitative agreement between calculated and observed spectra could be obtained when: (i) the non-radiative and radiative carrier recombination rates were approximately equal for nanocrystal sizes corresponding to visible emission, (ii) the spatial extent of the nanocrystal confinement potential is assumed to be slightly smaller than the measured size of the nanocrystal, and (iii) coalescence of individual nanocrystals produces electronic states corresponding to single nanocrystals with larger volume.